Electric Trailer Jack, recharge?

A family friend bought a second hand horse trailer.  

At the hitch area, instead of hand cranking up and down the trailer jack third leg, this trailer has electric.  Inside the trailer is a battery in a marine battery box.  When I was there to help her install and teach her a load leveling hitch, everything worked great.  She now tells me that hitting the switch to up or down does nothing like dead battery (she did not try with hooking up the trailer wiring.) 

I'll admit that I don't know much about these, and she knows even less.  When I was there, the switch worked even without the trailer wired to the car. 

• What recharges this battery?  
• Is there something more needed to make this recharge?
• Am I possibly just facing a weak battery that is not charging?

Usually there is a 12V feed in the round plug of the trailer wiring.  The truck alt will top it off when driving but if it sits too long the battery may be going flat if it's old.  I keep mine topped with a small solar panel.

I'd guess her Explorer doesn't have power on the 12v auxiliary pin on the trailer plug. Double-check that the fuse is installed; sometimes they aren't from the factory. 

What I am learning from y'all is when the truck is attached to the trailer, the truck charges this additional battery.  

I'll check the condition of the 7 blades and whether the charge actually charges.  

Thinking this through more, here is the actions of this trailer in her ownership.

• She drives 1 hour away to buy the trailer...all functions well with this electric jack.  She brings home this empty trailer on just a regular ball hitch
• About 2 weeks later, I help her in her driveway with attaching a WD hitch.  This entails lots of up and down action of the jack while trying to find the best ball height and other experiments.  All of this is done w/o the wiring connected so just using pure battery power.
• Her next 2 tows are 15 minute drives. Not much in the way of recharging.
• The battery is now dead.      

Now that I have more education, I think I'll educate her that use of the electric portion should happen when the trailer is attached to a running truck.  I'll also advise her that next time she is at the horse barn, where the trailer is kept, that she should eclectically attach her running truck to the trailer to give it some time to send some recharge to the trailer battery.   

If she is going to be making short runs or if the trailer is going to sit most of the time like most trailers she needs one of these.

https://www.amazon.com/ECO-WORTHY-Portable-Backup-Alligator-Adapter/dp/B017K6PH1S/ref=sr_1_3?dchild=1&keywords=solar+battery+charger&qid=1622987202&sr=8-3

I have one on my dump trailer, one on my Bobcat.

If it's like my wife's horse trailer (also a Featherlite) , there may be loading lights installed, controlled by an external toggle near the tail lights. 

On my wife's trailer, those are fed by the 12 volt feed through the trailer connector. If present, they might indicate whether that feed is active. 

Tom Suddard said:

I'd guess her Explorer doesn't have power on the 12v auxiliary pin on the trailer plug. Double-check that the fuse is installed; sometimes they aren't from the factory. 

Yeah, my '07 Chevy 2500HD was like that.

On my new F-250 there's a trailer battery control module that drives this pin.  It's got some smarts in it and only powers up when it detects a trailer, so putting a volt meter onto the pins may or may not tell you what you're looking for.  I think that module only came with the trailer tow package, though.

Also my impression is that this +12 line is really only intended for a relatively small battery, like the small ones intended for emergency electric brake use.  I would be careful hooking up a big car-sized battery to it, because if the battery is a low charge state it may pull more current through the line than the truck can support.

If the trailer is stored outside then a solar panel is the ideal solution.  I have a 100W panel on my trailer's roof and it means the trailer battery is just always charged without needing any attention on my part.